The present invention relates to semiconductor crystals, and, in particular, to indium phosphide bulk crystals, and, more particularly, to a method of growing twin-free crystals of the same.
One method of growing twin-free indium phosphide involves growth in the (111) direction using a growing angle less than 19.68 degrees from the vertical direction. The crystal produced by this method takes several hours to grow using the Liquid Encapsulated Czochralski process. The crystal has a long cone shaped upper portion and a significant amount must be wasted in cutting at 54 degrees to the growth plane to obtain (100) wafers necessary for device fabrication. U.S. Pat. No. 4,299,650 and U.S. Pat. No. 4,299,651 are incorporated by reference and also Bonner, W. A. "InP Synthesis and LEC Growth of Twin-Free Crystals," Journal of Crystal Growth, Vol. 54, 1981, pp 21-31.
Difficulties in forming twin-free InP in the (100) direction is related to crystallographic facets and the formation of small bubbles which appeared in the melt. These small bubbles are collected by the shear between the two melts and migrate to the outside edge of the crystal melt interface where they then attach to a growing facet to produce twins. The following article is incorporated by reference: Bachmann et al., "Liquid Encapsulated Czochraski Pulling of InP Crystal," Journal of Electronic Materials, Vol, 4, No. 2, 1975, pp. 389-406.
Thus there is a need for developing a method of producing bulk InP cystals having maximum useful wafers.